NAME

sysctl - read/write system parameters

SYNOPSIS

#include<unistd.h>#include<linux/sysctl.h>int_sysctl(struct__sysctl_args*args);Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION

Donotusethissystemcall! See NOTES.
The _sysctl() call reads and/or writes kernel parameters. For example, the hostname, or
the maximum number of open files. The argument has the form
struct __sysctl_args {
int *name; /* integer vector describing variable */
int nlen; /* length of this vector */
void *oldval; /* 0 or address where to store old value */
size_t *oldlenp; /* available room for old value,
overwritten by actual size of old value */
void *newval; /* 0 or address of new value */
size_t newlen; /* size of new value */
};
This call does a search in a tree structure, possibly resembling a directory tree under
/proc/sys, and if the requested item is found calls some appropriate routine to read or
modify the value.

RETURNVALUE

Upon successful completion, _sysctl() returns 0. Otherwise, a value of -1 is returned and
errno is set to indicate the error.

ERRORS

EACCES, EPERM
No search permission for one of the encountered "directories", or no read
permission where oldval was nonzero, or no write permission where newval was
nonzero.
EFAULT The invocation asked for the previous value by setting oldval non-NULL, but allowed
zero room in oldlenp.
ENOTDIRname was not found.

CONFORMINGTO

This call is Linux-specific, and should not be used in programs intended to be portable.
A sysctl() call has been present in Linux since version 1.3.57. It originated in 4.4BSD.
Only Linux has the /proc/sys mirror, and the object naming schemes differ between Linux
and 4.4BSD, but the declaration of the sysctl() function is the same in both.

NOTES

Glibc does not provide a wrapper for this system call; call it using syscall(2). Or
rather... don't call it: use of this system call has long been discouraged, and it is so
unloved that itislikelytodisappearinafuturekernelversion. Since Linux 2.6.24,
uses of this system call result in warnings in the kernel log. Remove it from your
programs now; use the /proc/sys interface instead.
This system call is available only if the kernel was configured with the
CONFIG_SYSCTL_SYSCALL option.

BUGS

The object names vary between kernel versions, making this system call worthless for
applications.
Not all available objects are properly documented.
It is not yet possible to change operating system by writing to /proc/sys/kernel/ostype.

SEEALSO

COLOPHON

This page is part of release 4.13 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this page, can be
found at https://www.kernel.org/doc/man-pages/.